While there have been improvements in detection, treatment and prevention techniques, dental caries remains a prevalent condition affecting people of all age groups. If not properly and promptly treated, caries could lead to permanent tooth damage and even to loss of teeth. Thus dental imaging based on an intra-oral camera is of great interest.
There exist known intra-oral cameras, such as those available from ACTEON Inc. of Mount Laurel, N.J., USA. Generally, intra-oral cameras are operated over a large working distance range that typically varies between about 1 mm to about 50 mm. They must also have a sizable depth of field (DOF), which is different at different working distances. Thus, focus adjustment is necessary to provide good image quality. However, for most of the known intra-oral cameras including the one disclosed in U.S. Pat. No. 6,019,721 (Holmes et al.), focus adjustment is performed manually by operator adjustment to the distance between a lens and an imaging sensor. Conventional intra-oral cameras must be separately adjusted for each image. This makes these conventional cameras poorly suited for obtaining images in the dental office and practitioners can find cameras without an autofocus capability more difficult to use.
System optics for intra-oral cameras must provide a large depth of field (DOF) and as wide a field of view (FOV) as is possible. Some of the existing intraoral camera use a small NA (numerical aperture) that can provide sufficient DOF (depth of field) to help reduce the requirements for focus adjustment. However, an optical system having a small NA has limitations and is poorly suited for providing the high resolution needed for dental examination. The small NA can be unable to provide sufficient luminous flux for intra-oral use.
A number of solutions that have been proposed for intraoral imaging use a liquid lens as part of the imaging optics. The liquid lens can adjust more readily to intraoral requirements and is advantaged with respect to FOV and DOF. Autofocus, however, remains a problem. Accordingly, there is a need to provide an intraoral camera having an auto focus capability that does not require additional components and that operates quickly enough for use in the dental office.